Transformers-Lec11.pptx

8/9/2019 Transformers-Lec11.pptx

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Three Phase TransformersEE3003 Electrical Machines I

By:A.Paranietharan

Electrical Engineer

Ceylon Electricity Board


2/41

Winding connections

Standard terminal maring of !" # $" %indings of 3Phase Transformer&

'ote: ( "oltage ind)ced in all %indings in a gi*en leg are in(+hase ,-eca)se all

are %o)nd in the same sense

There are three di/erent o+tions of connections&

Star

1 2elta

3 ig(4ag

A A1

B B1

C C1 c c1

- -1

a a1


3/41

Winding connections . . .

. Star

A

A1

B

B1C

C1

"oltage Phasors 5 Star connection

A A1

B B1

C C1

'


4/41


1. 2elta

A

A1B

0

B1

C0

C1

"oltage Phasors 5 2elta connection

A A1

B B1

C C1


5/41


3. ig(4ag

A6

A3

B6

B3

C6

C3

"oltage Phasors 5 ig 4ag connection

C

C1

B

B1

A

A1

A A1

B B1

C C1

A3 A6

B3 B6

C3

C6


6/41


ig(4ag . . .*oltage %ise 4ig(4ag connection gi*es only 78.89 star

*oltage. !o%e*er& 4ig(4ag connection has *ery )sef)l

as+ects s)ch as for creating articial ne)tral +oint in an

isolated +art of a system ,e.g. Earthing transformer&

s)++ressing harmonics in case of harmonic rich loads ,Po%er

Electronic con*erter systems etc.


7/41

Per +hase e;)i*alent circ)it

r5 Primary %inding resistance +er +hase


8/41

"ector Sym-ol

The follo%ing shall -e s+ecied to identify a transformer in f)ll&. $ine *oltage ratio

1. M"A ca+acity

3. "ector sym-ol

e.g. 33? "& @M"A& 2y transformer


9/41

"ector Sym-ol

"ector sym-ol has three +arts&

a ++ercase letter ,2& or signifying !" connection ,2elta&

Star or ig(4ag

- $o%ercase letter ,d& y or 4 signifying $" connection

c "ector n)m-er re+resenting the +hase shift of $" side line

*oltage %ith res+ect to !" side line *oltage

( standard *ector n)m-er is gi*en as the !o)r('o ass)ming

long hand ,min)te hand to -e at cloc +osition 1.

or e


10/41

"ector Sym-ol . . .

Hour NoPhase shift of LV line voltage

w.r.t HV line voltage

0 0

8 70

( 30

D30


11/41

"ector Sym-ol . . .

E.g.d

( !" side is in stard 5 $" side is in delta

5 $" line *oltage is 30 lagging !" line *oltage

If %e ha*e tertiary %inding too& the *ector sym-ol m)st contain its

information too.

E.g:y0d

( !" side is in star

y 5 $" side is in star

0 5 $" line *oltage in(+hase %ith !" line *oltage

d 5 tertiary in delta

5 tertiary line *oltage is 30 leading !" line *oltage


12/41

Classes of 3 +hase transformers:

There are fo)r ,06 -asic classes&. Class transformers

1. Class 1 transformers



The -asis of classication is +hase shift ,of $" line *oltage %.r.t

!" line *oltage


13/41

Classes of 3 +hase transformers . . .

Class transformers 0+hase shift

Class 1 transformers 70+hase shift

Class 3 transformers ( 30+hase shift

Class 6 transformers D 30+hase shift


14/41

Winding Interconnections

Each %inding in a transformer is ins)lated to %or at some

*oltage rating and %e m)st ens)re that this rating is not

eect to this constraint %e can decide any

s)ita-le interconnection.

To +)t in a di/erent %ay %e can determine the

interconnection as +er the gi*en *ector sym-ol.

Some of these interconnections are ill)strated in the follo%ing

slides&


15/41

Winding Interconnections . . .

Yy0A1

A

B1

BC

1

C

"ector 2iagram

a1

a

-1

-c1

c

a1 a

-1 -

c1 c

A A1

B B1

C C1

Terminal connectio


16/41


Dd0

B

B1

C

C1

"ector 2iagram

A A1

B B1

C C1

a1 a

-1 -

c1 c

Terminal connection


17/41


Yy6A1

A

B1

BC

1

C "ector 2iagram

a

a1

-

-1

c0

c1

a a1

- -1

c c1

A A1

B B1

C C1

Terminal connection


18/41


Dy1

A0

A1

B0

B1

C0

C1

"ector 2iagram

a1 a

-1 -

c1 c

a1

a0

-1 -0

c1

c0

A A1

B B1

C C1

Terminal connectio


19/41


Dy11

A1

A0

B1

B0

C1

C0

"ector 2iagram

a1

a0

-1

-0

c1

c0

a1 a

-1 -

c1 c

Terminal connection

A A1

B B1

C C1


20/41


Dz0

"ector 2iagram

A1

A0

a6

a3

c6

c3

c0

c1a1

a6 a3

-6 -3

c6 c3

a1 a

-1

-

c1 c

A A1

B B1

C C1

Terminalconnection


21/41


i. Zy1

ii. Zy11

iii.Yd11

iv.Yd1


22/41

E/ects of %rong +olarity connectionWhen connecting transformer terminals es+ecially +olarity

connections& %e

sho)ld not mae errors& the conse;)ences may -e either fatal to

the

transformer or )ne


23/41

E/ects of %rong +olarity connection . . .

A1

A

B1

BC

1

C

a1

a

-1

-0

c1

c0

a1 a

-1 -

c c1

A A1

B B1

C C1

Erroneo)s connection %ith$" %inding cc1 connected%ith %rong +olarity

It res)lts& )n-alanced3+hase $" o)t+)t.Also +hase shiftamong 3 +hases are)n-alanced.


24/41

E


25/41

Magneti4ation -eha*io)r of 3 +hase transformers

Magneti4ation:

To magneti4e a transformer means to set magnetic F)< in its iron

core.

Ty+ical Magneti4ation C)r*e

The iron core has a non(linear magnetic -eha*io)r # this leads to

either non(linear magneti4ing c)rrent or non(linear magnetic F)


26/41

Magneti4ation -eha*io)r of 3 +hase transformers . . .If the a++lied *oltage is sin)soidal then the ind)ced emf and

hence F)< %ill -e sin)soidal. 'on(linear Im?-eha*io)r then

res)lts in a non(sin)soidal Im. i.e. !armonic rich Im. The dominant

is third harmonic c)rrent.

Im

Im


27/41

Magneti4ation -eha*io)r of 3 +hase transformers . . .

The gra+h in red sho%s magneti4ing c)rrent containing a

signicant amo)nt of 3rdharmonic com+onent can -e as

high as 109 of f)ndamental com+onent.


28/41


Gn the other hand& if magneti4ing c)rrent Imis sin)soidal the

res)lting F)< %ill contain harmonics

l)< %a*eforms -ecomes some%hat Fat(to+ %a*eforms

containing 3rdharmonics.

Im


29/41


This harmonic rich c)rrent or F)< can inF)ence the

o+eration of a three +hase transformer. !armonic F)

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Transformers-Lec11.pptx